1. Field of the Invention
This invention relates to a control unit for technical installations, devices and/or machines having a microprocessor, a programmable memory, a housing and at least one data line leading out of the housing for connection with an external device for writing data to the programmable memory.
2. Description of the Background Art
Such control units based on microcontrollers are meanwhile used in a great number of machines and devices, for example in automobiles or consumer electronics, etc. The control program required by the microprocessor is usually deposited in a programmable memory. In many cases, said memory is at least partly a freely programmable, erasable and overwritable memory. The control unit can then be adapted anytime to customer and application needs by changing the required data and optionally also complete program runs. This subsequent change also allows in particular later improvement or updating of the control program. In particular, it is thus possible to change the control software to subsequently modify for example the functional and/or performance range of the control unit and thus the entire technical installations of the device or machine. Reprogramming is usually done by connecting an external device to a data line leading out of the housing and then writing the required data to the programmable memory over the data line. The external device is often a special device for programming the particular control device. However, it can also be a commercial computer provided with special software for programming the control unit. The data lines can be data lines specially provided for programming that allow a write access to the programmable memory. However, they can be data lines also used by the control unit for controlling the technical installation and/or machine, i.e. data lines having a double function.
A disadvantage of a later possibility of changing the control software is that unauthorized persons can abuse said possibility and for example illegally modify the functional and/or performance range of the control unit subsequently and thus “tune” the entire technical installation or machine. This has firstly the disadvantage for manufacturers that they could suffer losses through tuning-induced damage in the period of guarantee and the resulting costs. Additionally, the product differentiation features can be changed by unauthorized persons subsequently to such an extent as to lastingly interfere with the particular manufacturer's trademark positioning and trademark policy.